Bentonite nodules

ABSTRACT

Compressed bentonite-containing nodules are disclosed as are methods for their production and methods for using them to plug wells.

This application is a divisional of U.S. Ser. No. 09/964,930 filed Sep.26, 2001, now U.S. Pat. No. 6,820,692; which application claims thebenefit of U.S. Provisional Application No. 60/237,945 filed on Oct. 3,2000, now abandoned. Each of these applications are incorporated hereinby reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to filling or plugging wells.In particular, the present invention relates to improved materials forplugging wells such as drill holes within the earth and for maintainingthe plug integrity indefinitely, methods for preparing the materials andmethods for using the materials.

2. Description of the Related Art

It has been well known to provide deep (on the order of several hundredfeet to thousands of feet) and shallow (on the order of twenty toseveral hundred feet) wells such as drill holes within the earth for avariety of purposes. Relatively shallow drill holes are formed duringseismic exploration, water wells, monitoring wells, cathodic protectionwells and mineral exploration and extraction wells and other purposes.Deeper holes are typically formed during standard oil, gas, and/ordisposal well operations. A deep drill hole is formed and then linedwith a casing. The drill hole generally passes through severalcompositions, such as hard compacted soil, clay, loose sand, and othertypical geologic materials, in addition to one or more water-bearinglayers. Such water-bearing layers may represent a saline water source ora fresh water aquifer. Once the well bore is determined to be unusable,the well bore is abandoned. If left unsealed, gases and/or liquidsescape from the zones of origination and migrate through the hole.Further, the casings corrode and disintegrate causing additionalmigration pathways.

In particular, a fresh water aquifer may “leak” through the casing andhole into a fracture or uncharged zone, causing loss of water from theaquifer. A drill hole extending between a saline water source orpetroleum and a fresh water aquifer may allow commingling of thesezones, damaging both. Additionally, contamination from the surface maycause damage, such as contaminated water passing downward through thehole and casing into a fresh water aquifer. These problems can alsooccur with shallow holes.

To overcome these problems it has been known to plug the casings anddrill holes with cement. However, cement has proven less than effectivein maintaining the integrity of the seal throughout the casing over longperiods of time. One problem with cement plugs is that voids can occurduring placement of the cement slurry in the casing as a result ofincomplete displacement of drilling fluids by the slurry. In addition,cured cement is brittle and can crack over the life of the plug due topressure changes or due to earthquake activity. Cured cement undergoesstrength retrogression at temperatures above 230° F. if the cement doesnot contain additional silica. All of these factors can contribute tolimited success with cement plugs.

In the past, sodium bentonite has been proposed for filling drill holes.Early work focused on the use of finely ground bentonite for fillingrelatively shallow holes. A report entitled “Axial Shear StrengthTesting of Bentonite Water Well Annulus Seals” by Fred Lee Ogden andJames F. Ruff published by Colorado State University, 1989, discussesthe use of bentonite as an annulus sealant. Past usage of bentonite isexplained in a report entitled “Experiments in Subsurface Applicationsof Bentonite in Montana” by John Wheaton, Steve Regele, Bob Bohman, DaveClark and Jon Reiten, published by Montana Bureau of Mines and Geology,1994. Both of the foregoing reports are incorporated herein byreference.

When bentonite as ⅜″ in diameter or smaller chips is poured into a holeit begins to expand when exposed to water. This method is adequate forshallow holes since the bentonite sinks to the bottom of the hole beforea significant amount of swelling occurs. However, if bentonite is pouredinto deep well holes, the hole may contain several hundred feet ofwater.

In general, high-grade and low-grade bentonite chips fall through waterat an average velocity of about 1 ft/sec. Smaller bentonite granules of⅜″ in diameter or less fall more slowly than larger particles for tworeasons. First, smaller particles have more surface area per unitweight, and therefore proportionally more drag in the water. Alsosmaller bentonite granules are typically less dense than larger chips. Abentonite granule with a diameter of ⅜″ may have a volume of 0.5 cm³ andweigh 1.01 grams, while a bentonite chip with a ¾″ diameter weighs 3.65grams and has a volume of 1.50 cm³. In this example, the smaller granulehas a density of 2.02 gr/cm³ and the larger chip has a density of 2.43gr/cm³.

Once hydration begins, the density (or specific gravity) of the granuledecreases as the granule swells. Similarly, the fall velocity of thegranule in water decreases at a rate of about 0.009 ft/sec per minute offall. For instance, a small granule having an initial fall velocity inwater of just under 1 ft/sec, after 44 minutes of exposure to water,will fall at a rate of approximately 0.6 ft/sec. As the granule absorbswater, its density decreases approaching the density of water furtherslowing the fall velocity. These factors prevent small granules fromeffectively being used to plug deep holes with several hundred feet ofwater therein.

U.S. Pat. No. 5,611,400 of James et al. describes the use of coarse drydehydrated ground chips of sodium bentonite as a well plugging material.The chips are from ¼″ to about 2″ in size. U.S. Pat. No. 5,810,085 ofJames et al. describes the use of large pieces of bentonite having aminimum diameter of at least ⅞″ and up to at least about 3 inches as awell hole-plugging material.

These patents describe relationships between particle size and particleperformance during well plugging. They point out that each particleexpands at a rate proportional to the liquid content of the particle.The rate of hydration of a given particle is related to the surface areaof the particle and the volume of the particle. However, the volume andthe surface area of a particle vary with respect to the particlediameter. The ratio of particle surface area to particle volume decreaseas the particle diameter increases. Accordingly, the rate of hydrationdecreases (as does the rate of expansion) with increased particlediameter.

As noted above, it is desirable that the particles have a diameter of atleast ⅞″. A particle with a diameter of less than ⅞″ hydrates and mayexpand too rapidly to allow the particle to reach the bottom of a deephole before plugging the hole. By way of example, fine bentoniteparticles with a ⅜″ diameter may hydrate and swell to 10 times theiroriginal size and turn to a slurry state in less than 15 minutes. Oftendrill holes are several hundred feet deep with over a hundred feet ofliquid. Each particle falls at a rate dependent upon the particle'sdensity and the liquid's viscosity. However, generally the density ofthe bentonite and the viscosity of the liquids within the holes are suchthat a particle having ⅜″ diameter falls at a rate of one foot persecond. As the particle swells, its density decreases and its surfacearea increases, further reducing its fall velocity. Such particlesrequire several minutes to reach the hole's bottom. Accordingly, ⅜″particles may swell and plug the hole before reaching the bottom or turnto a slurry state.

Another factor which plays a part in the use of bentonite as a materialfor plugging wells, drill holes and the like is salinity. Saline wateris found in many wells. High salt contents in saline water can interferewith bentonite particles by promoting breakdown and flaking which couldreduce the density of the plug when hydrated. A preferred form ofbentonite would minimize these problems.

Large-particle bentonite materials have been formed heretofore as chunksand as extrudates. Chunks are accompanied by a large quantity of fineswhich must be removed. Chunks are irregular and often lead to bridging.Extrudates are difficult and slow to manufacture. They often lackphysical integrity.

There is a need for an optimal large particle form of bentonite which isconvenient to use, inexpensive to form, strong and durable whichrequires minimal removal of deleterious fines.

Listing of Background Materials

-   U.S. Pat. Nos.-   2,609,880-   4,886,550-   4,936,386-   5,195,583-   5,657,822-   5,810,085-   “Bentonite as a Waste Isolation Pilot Plant Shaft Sealing Material”,    Contractor report, SAND 96-1968 Unlimited Release UC-721, Jaak    Daemen and Chongwei Ran, University of Nevada-Reno, December 1996.-   “Bentonite Well Plugging Technique”, from Field Applications    publication by RMOTC, February 1998.-   “Cement Sheath Stress Failure”, SPE 20453, Goodwin and Crook,    September 1990.-   “Experiments in Subsurface Applications of Bentonite in Montana”,    Wheaton et al., 1994.-   “Friction Factors for Hydrated Bentonite Plugs”, SPE 38347, Towler &    Ehlers, May 1997.-   “Geosynthetic Clay Liners Permeated with Chemical Solutions and    Leachates”, Journal of Geotechnical and Geoenvironmental    Engineering, Ruhl & Daniel, April 1997.-   “Hydraulic Conductivity of Compacted Bentonite-Sand Mixtures”,    Canadian Geotechnical Journal, Volume 29, Number 3, Kenney et al.,    June 1992.-   “Report-Axial Shear Strength Testing of Bentonite Water Well Annulus    Seals”, State University, Ogden & Ruff, Fall 1989.-   “Sustained Casing Pressure in Offshore Producing Wells”, OTC 11029,    Bourgoyne et al., May 1999.-   “Using Coarse Ground Bentonite to Plug Abandoned Holes”, Melvyn    James, in WWJ, June 1996.-   Handbook on Well Plugging and Abandonment, Pennwell Publishing    Company, Dwight K. Smith, 1993.-   “Hydraulic Conductivity Tests on Compacted Clay”, Journal of    Geotechnical Engineering, Boynton, S. S. & Daniel, D. E., 1985.-   “Mineral Water Interactions and Their Influence on the Physical    Behavior of Highly Compacted Bentonite”, Canadian Geotechnical    Journal, R. Pusch, 1982.-   “State of the Art Evaluation of Repository Sealing Materials and    Techniques”, Materials Research Society, Gnirk, P. 1988.-   “The Effects of Brine Contamination on the Properties of Fine    Grained Soils”, Geotechnical Practice for Waste Disposal '87,    Proceedings of a Specialty Conference, Ho, Y. A., Jun. 15–17, 1987.-   “The hnpact of a NaCl Brine on the Behaviour of Compacted Fine    Grained Soil”, University of Windsor, Department of Civil    Engineering, Ridley, K. J. D., Bewtra, J. K. and Mccorquodale, J. A.    1983.-   “Abandoned Wells”, paper by Maurice James, January 2000.-   “Comments on Petro-Plug's Proposed Procedure for Sealing Abandoned    Oil Wells”, prepared for Maurice James by David DeGroot (UMASS at    Amherst), Mar. 14, 1998.-   “Evaluation of Dispersion Characteristics of Bentonite with    Application to Design of Containment Transport Barriers”, DeGroot et    al., August 1998.-   “Plugging of C-1 & C-2 Monitor Wells-I Area”, Memorandum from L. A.    Sessions to G. A. Johnson, Jan. 14, 1997.-   “Report of Pressure Tests, Plugging Simulations”, Accord    Technologies, Ehlers, March 1999.-   Comments from Dr. Roland Pusch to Craig Gardner regarding “Well    Abandonment, Compressed Bentonite Questions”, Ideon Research Center,    SE-22370 Lund, Sweden, June 2000.-   “Design and construction of a prehydrated sand-Bentonite Liner to    contain Brine,” M. D. Haug, Barbour and Longval, 1988.-   Letter and Report to Maurice James from Jerry Thornhill (Consultant)    providing results from USEPA's Robert S. Kerr Environmental Research    Center's Mechanical Integrity Testing Facility near Ada, Okla.-   Letter of Support to Maurice James from Clark Turner (Director, NPR    sites in Colorado, Utah and Wyoming), Jan. 8, 1998.-   Letter to Gordon Fassett (Wyoming State Engineer) from Don Lamborn    (Environmental Specialist) at the Pittsburg & Midgway Coal Mining    Co. (a Chevron Company).-   Letter to Maurice James from Jack Daemen (Professor and Chair of    Department of Mining Engineering at University of Nevada-Reno), Mar.    22, 1998.-   Letter to Maurice James from R. Odell (Consulting Geologist,    Minerals Scout of Rocky Mountain Scout), Aug. 22, 1999.-   Petro-Plug Project Test Results, RMOTC, Tyler. Jan. 5, 1998.-   Predicting Hydraulic Conductivity of Clay Liners, David E. Daniel.-   Report of Well Test, Accord Group Inc., Ehlers, Oct. 27, 1997.-   “Soft Sell Project Preliminary Results from the Coalinga Abandonment    Pilot”, Chevron Environmental Management Company.-   Technical Note, Accord Group Inc., Ehlers, Oct. 29, 1997.-   “Swelling Pressure of Highly Compacted Bentonite”, University of    Lulea, Div. Of Soil Mechanics, Pusch, R., 1980.-   “Preliminary Report on Longevity of Montmorillonite Clay under    Repository—Related Conditions,” Lund University of Technology,    Pusch, R., 1990.-   “Permeability, Swelling, and Radionuclide—Retardation Properties of    Candidate Backfill Materials,” Symposium on Scientific Basis for    Nuclear Waste Management, Westsik, J. H., et.al., 1981.-   “New Abandonment Technology New Materials and Placement Techniques”,    Society of Petroleum Engineers #66496, Englehardt, J., et.al., 2001.-   “Waste Isolation Pilot Plant Hazardous Waste Permit”, U.S.    Environmental Protection Agency I.D. Number NM4890139088, Issued to    U.S. Department of Energy, 2000.

SUMMARY OF THE INVENTION

An object of this invention is to provide bentonite-based materialswhich have properties which make them particularly suitable for pluggingdrill holes. Such materials should have adequate strength and durabilityto be used in drill hole plugging procedures without unacceptable levelsof degradation and breakage.

Another object of this invention is to provide methods for preparingbentonite materials into forms which are useful for plugging wells anddrill holes.

Yet another object is to provide such methods for manufacturing formedbentonite materials which are efficient and easily employed on acommercial scale.

An additional object of this invention is to provide methods forplugging wells and drill holes using these formed bentonite materialswhich methods are reliable when applied to a wide variety of hole depthsand configurations and which are effective in a variety of environments.

These and other objects are achieved by a new form of bentonite drillhole plugging material. This material is in the form of compactednodules and contains bentonite and water as essential ingredients andoptionally contains other nonbentonite solids. The bentonite and waterare in admixture with the proportion of water to permit the formation ofcompacted nodules having a mean particle survival at a crush force of atleast 800 newtons and an at least 50% survival when dropped 1.5 metersonto a concrete surface. These compacted nodules of bentonite have aspecific gravity greater than 2.0. These nodules have rounded contoursand typically may be described as pillows, as spheres or as flattenedspheres. In one aspect this invention relates to this compacted nodulematerial.

In another aspect, this invention relates to methods for forming thesenodule materials. These are continuous methods and involve

-   -   a. obtaining a feedstock comprising bentonite in admixture with        a proportion of water to permit the formation of compacted        nodules having a specific gravity greater than 2.0, a mean        particle survival at a crush force of at least 800 newtons and        at least 50% survival when dropped 1.5 meters onto a concrete        surface,    -   b. feeding the feedstock under pressure to a continuous roll        press machine under conditions to permit the formation of said        compacted nodules and    -   c. recovering the compacted nodules.

In an additional aspect, this invention provides methods for pluggingdrill holes. These methods involve introducing a plurality of nodulesinto the drill hole, the nodules containing bentonite in admixture witha proportion of water to permit the formation of compacted noduleshaving a mean particle survival at a crush force of at least 800 newtonsand at least 50% survival when dropped 1.5 meters onto a concretesurface, and thereafter permitting the feed nodules to come in contactwith water in an amount and for a time adequate to cause the nodules toswell and form a substantially hydraulically solid plug in the drillhole. In some of these methods the drill hole is empty and the nodulesfall easily and directly to the bottom of the hole. In other methods thedrill hole may contain liquids. In the case where the liquid is viscous,it may be advantageous to warm the liquid, or displace the liquid suchas by adding hot water, in order to assure that the nodules fall throughthe viscous liquid to the bottom of the drill hole.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention will be described in more detail with reference to thedrawings. In these drawings

FIG. 1A is a side view of a representative compacted bentonite nodule ofthe invention. FIG. 1B is a top view of the same nodule.

FIG. 2A is a side view of a second representative compacted bentonitenodule of the invention. FIG. 2B is a top view of the same nodule.

FIG. 3A is a side view of another representative compacted bentonitenodule of the invention. FIG. 3B is a top view of the same nodule.

FIG. 4 is a cross-sectional view of a roll pressing apparatus useful informing the nodules of this invention and useful in practicing themethods of making of this invention.

FIGS. 5A, 5B and 5C are three not-to-scale cross-sectional views ofdrill holes plugged with the nodules of this invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

In accord with this invention, bentonite feedstock is formed intonodules which are useful for plugging drill holes. In this sectionpreferred embodiments of this invention will be described. This sectionis broken into several subsections as follows:

-   -   The Bentonite Feedstock    -   The Nodules    -   Process for Preparing    -   Process for Plugging Wells        The Bentonite Feedstock

Bentonite is a naturally-occurring clay containing the clay mineralsmectite. It typically also contains accessory minerals such as quartz,mica, feldspar and calcite. Sodium bentonite is a common form of themineral and is the form used herein. Sodium bentonite is primarily minedin Wyoming. Calcium bentonite is also available and often is intermixedwith sodium bentonite in naturally-occurring deposits. Bentonite inwhich sodium bentonite predominates is preferred.

Naturally-occurring bentonite contains approximately 6–7% by weightconnate water. This water is bound into the bentonite and is not easilyremovable by natural drying. Bentonite includes variable amounts ofnonconnate water which is in addition to the connate water. Thisnonconnate water ranges from 0% by weight of such water up to as much as15 or 20% by weight based on the total weigh of water plus bentonite.The amount will depend on the conditions of the mineral deposit, how thematerial is dried after mining, and the humidity and temperature of theenvironment in which the mineral is stored and used and the like.

In the practice of this invention, the water content of the bentonite iscontrolled. In describing this controlling, the connate water is notincluded in water values. Thus, “bentonite” or bentonite having “0%”water”, has no additional water added by the manufacturing process butdoes have the 6–7% of connate water. Bentonite with “7%” water by weighthas the 6–7% connate water plus 7% added water for a total of 13–14%water by weight. When the word “bentonite” is used herein without anyqualifiers as to water content, it is intended to mean bentonitecontaining the 6–7% by weight of connate water.

Bentonite is available commercially as a dry material (water content0%). It has a bulk density when loose of about 1.1 g/cm³. Whencompacted, its density is higher. Bentonite is also available as anundried or partially dried material having measurable water levels (forexample 2–8%). In the present invention bentonite is fed under pressureinto a roll pressing apparatus. Accordingly, the bentonite should besubstantially devoid of large intractable solids such as rocks or thelike. Preferably the bentonite used in this invention passes through an8 mesh screen.

The bentonite can be used in a substantially pure, as mined, state. Itcan also be used in admixture with minerals not typically present innatural bentonite such as barite (another clay mineral) or the like.Barite has a higher specific gravity than bentonite and can be added toincrease the specific gravity of the resulting nodules. This can assistin speeding the descent of the bentonite nodules to the bottom of adrill hole, particularly in cases where the drill hole contains water orother liquids. These materials are referred to as “nonbentonite”minerals or solids.

Nonmineral materials can be added to the bentonite feedstock to alterthe characteristics of either the nodules themselves or the plug thatforms when the nodules contact water and swell. These materials arereferred to as “additional materials” and have been described in theliterature of well drilling and well sealing heretofore and include, forexample, wood chips, walnut shells, cellophane strips, nylon chop, wooland the like.

Nonbentonite solids are completely optional components of thefeedstocks. Typically they are less than half the total solids. Thus theproportion of nonbentonite solids/bentonite can range from 0/1 to 1/1and more commonly can range from 0/1 to 0.5/1 by weight.

The feedstock always contains the connate water and may containadditional water above the connate water. The amount of additional wateris controlled to provide the desired durable nodules and to permit theirproduction in standard roll press equipment. The amount of additionalwater, as a weight percentage, based on the weight of added water plusbentonite is from about 2% to about 20%, preferably from about 5% toabout 20%, more preferably from about 10% to about 20% and especially 12to 16%.

Thus, overall feedstock compositions are as follows:

Bentonite  35 to 98% by weight Nonbentonite minerals   0 to 45% byweight Water (nonconnate) 2.0 to 20% by weight Preferably, Bentonite  45to 95% by weight Nonbentonite minerals   0 to 35% by weight Water(nonconnate)   5 to 20% by weight more preferably, Bentonite  50 to 90%by weight Nonbentonite minerals   0 to 30% by weight Water (nonconnate) 10 to 20% by weight. and especially, Bentonite  64 to 88% by weightNonbentonite minerals   0 to 20% by weight Water (nonconnate)  12 to 16%by weight.

As noted above, the feedstock can contain additional materials, ifdesired.

The Nodules

The bentonite-containing feedstock is formed into nodules for use as awell hole-plugging material. As used herein, a “nodule” is defined to bea solid continuous body having substantially its entire exterior surfacecompacted smoothly into a rounded shape. As shown in FIGS. 1 through 3,the nodules can have a variety of shapes. To achieve efficient use indrill hole plugging operations, it is desirable that the nodules havegenerally rounded surfaces. This assists in achieving dense packing inthe drill hole and tends to minimize bridging in the drill hole. Onecommon shape, a “pillow” shape, is shown in FIGS. 1A and 1B. As can beseen, this shape presents rounded corners and is somewhat squared off intop view. In this nodule the largest cross-sectional dimension isdenominated DM and the smallest dimension is denominated Dm. Duringproduction of nodules in a roll press, DM is the dimension across theface of a roll press cavity and Dm is the combined “depth” or“thickness” of the two cavity halves.

Another possible nodule shape is substantially spherical. Our resultssuggest that a true sphere would give excellent down-hole sealingperformance. Such a shape is shown in FIGS. 2A and 2B. Again DM is thelargest dimension. It is often difficult to get good, complete fillingof true spherical nodule-forming cavities in a roll press. Accordingly,for this practical reason, it is preferred to use nodules having asomewhat flattened spherical cross-section. Such an “oval” or“elliptical” cross-section nodule material is shown in FIGS. 3A and 3B.As can be seen from these drawings, the ratio of DM:Dm can range fromabout 1:1 (as shown in FIG. 2) to about 2:1 or 3:1 as shown in FIGS. 1and 3. We have had best results in terms of nodule compaction, rollpress cavity fill and consistent release from the roll press cavitieswhen the ratio DM:Dm is from about 1.01:1 to about 3:1, preferably about1.05:1 to about 2.5:1 and especially from about 1.5:1 to about 2.25:1.

The size of the nodules is controlled. When the nodules are to be usedas a well plugging material the preferred minimum size for DM is about⅞″. The maximum size for DM depends in part upon the diameter of thedrill holes and wells in which the nodules are to be used. Typically, DMshould not exceed about 0.67 times the diameter of the drill hole andpreferably should not exceed 0.6 times the drill hole diameter. Manycommon drill holes are from about 5″ to about 8″ in diameter but somewells can reach 18″ or 24″ or greater in diameter. Our work has focusedon plugging 5″ to 8″ diameter wells and with the largest nodules we havemade, DM has ranged up to about 3 to 4 inches. For this size drill hole,and considering the sizes of cavities which can be easily employed in aroll press, the preferred sizes for DM range from about 1″ to about 5″,more preferably from about 1.5″ to about 4″ and especially from about 2″to about 3.5″.

While these materials have worked well, one could envisage largernodules (DM equals up to 6″) for use in larger diameter wells.

Many of the advantages of the high strength compacted nodules of thisinvention are also realized with smaller sizes such as nodules having ¼″to about ⅞″ DM values. These smaller nodules can be used for wellplugging as herein described and can also find application in morespecialized sealing operations such as sealing or plugging betweencoaxial casings or anular sealing around joints in a casing string. Inthese applications, their smaller size can be advantageous.

The nodules of this invention should be durable. If they are fragile anunacceptable proportion of fines and shards will form during normalhandling and drill-hole-filling procedures. It has been found that if,on average, the nodules have a mean particle survival at a crush forceof at least 800 newtons and can survive at least 50% of all drops of 1.5meters onto a concrete surface, they will give acceptable performance asa drill hole plugging material. More preferred nodules can withstand100%, of all 2 meter drops and have a mean particle survival at a crushforce of at least about 900 newtons.

The nodules have a controlled high density as a result of thecompacting. Their density ranges from about 2.00 g/cm³ to about 2.5g/cm³ and preferably 2.05 g/cm³ to 2.25 g/cm³. If substantial amounts of“additional materials” were added this could lower the density below 2.0g/cm³. This would generally not be desirable.

Process for Preparing

The nodules are formed by compressing the feedstock into a forming mold.This can be carried out in a roll press. As shown in FIG. 4, a rollpress includes a pair of rolls 1A and 1B which are driven in oppositedirections. The clearance between the rolls can be adjusted such as byhydraulic system 4. This can adjust the degree of compaction applied tothe feedstock when it is formed into the nodules.

Each of the rolls carries a plurality of cavity halves, such as cavityhalves 2 a, b, c and d on roll 1 a and cavity halves 2 e, f, g and h onroll 1B. These cavities are positioned so that as the rolls turn, cavityhalves pair up to create a cavity corresponding in shape to the shape ofthe final nodule. In FIG. 4, cavity halves 2 d and 2 h are depictedforming such a cavity.

Feedstock is placed in feed hopper 10 and fed to the rotating rolls byscrew feeder 5. The feedstock fed via screw drive feeder 5 passes thoughfeed adapter 7 which is designed and sized to direct the proper amountof feed to the cavities as they are being formed. The clearance betweenthe feed, adapter and the rolls and the relative velocity of the screwdrive can be varied to adjust the pressure applied to the feedstockduring compaction into nodules. 6 is a bearing block for the drive. 9 isa paddle mixer in the feed hopper which assures proper filling of thedrive screw. The nodules, such as shown as 3, when formed, are ejectedfrom the rollers and are collected in product chute 8.

The feedstock is compacted under pressure. This is a pressure of atleast about 1 MPa, preferably at least about 3 MPa and especially atleast about 5 MPa, such as from about 5 MPa to about 20 MPa. The rollpress is operated at a speed of from about 2 RPM to about 50 RPM,preferably 3 RPM to about 40 RPM and especially 5 to about 25 RPM beingmost common.

The roll press will generate substantial heat due to friction resultingduring the compaction process. This is usually acceptable and may causethe outer surfaces of the nodules to dry and anneal slightly. If heatingbecomes excessive, heat can be removed by means not shown.

Process for Plugging Wells

The nodules of this invention are used for plugging wells. A “well” isdefined by the United States Environmental Protection Agency to be ahole in the ground that is deeper than it is wide (40 CFR). Thatdefinition is used herein, as well.

Representative wells plugged in accord with the invention include drillholes made in connection with oil and gas exploration and extractionincluding production wells, injectors, seismic holes, and the like.Other representative wells include drill holes and shafts produced inconnection with mineral extraction, water production and waste disposal,to name but a representative sample.

In this use, nodules are introduced into the drill hole or other well bypouring or pumping and allowing the nodules to free fall to the bottomof the drill hole. They can be introduced using water-permeable sleeves,copper carriers, and the like. The nodules can be suspended in a fluidsuch as water or a mud, such as a bentonite-containing abandonment mudand injected to the desired location using pumps or the like.

In one application, the bentonite nodules can be placed over the entirelength of a well, substantially filling it and providing a bentoniteplug over the entire length of the drill hole.

As illustrated in FIG. 5A, in another application, the bentonite nodulescan be placed at the top and bottom of a drill hole or other well. Anonbentonite material can be used between the two layers of nodules tosupport the top layer until it swells.

As illustrated in FIGS. 5B and 5C, in other applications the bentonitenodules can be placed at the top and bottom of a drill hole and at otherlocations in the drill hole to achieve plugs between various formationsor layers.

When using the compressed bentonite nodules of this invention to plugdrill holes it sometimes happens that a layer of higher viscosity liquidis present in the drill hole or other well. This is most commonly alayer of crude oil floating upon a layer of water in the drill hole. Inthis case, the viscous oil layer may provide resistance to the nodulesor other solids, such as gravel, and prevent them from easily falling tothe bottom of the drill hole. The bentonite nodules detained by the oillayer can pick up water, swell and bridge the drill hole at aninappropriate depth. Adding heat to the drill hole prior to adding thebentonite nodules can be helpful in solving this problem as the heatreduces the viscosity of the oil layer and decreases the likelihood thatthe nodules will be held up for a long period in the oil layer.

Heat may be added in any manner. This could include passing a flow ofsteam or hot gas into the oil layer. However, most drill hole pluggingoperations take place in settings where drill holes are being abandoned.Thus the drill hole typically does not have pipes or other means fordelivering steam or hot gas to the oil layer. In addition, there isoften no equipment on site for producing steam or hot gas. In thesesettings, however, it is often possible to obtain hot water. Hot watercan simply be poured into the drill hole to warm the oil layer.

In a drill hole setting, hot water is most commonly from about 115 toabout 180° F. and more typically from 125 to 175° F. and especially 130to 150° F. One can add from about 1 to 10 barrels of hot water to adrill hole while larger amounts of up to about 100 barrels can also beused if desired.

The amount of heating is often varied to suit the particularcircumstances of a particular drill hole. A large excess of heating istypically not the answer as it takes extra time and involves unneededexpense. In addition, it also can lead to conditions where anunnecessarily elevated temperature causes the bentonite to expand toorapidly when a bentonite nodule is traversing the oil layer which can inturn lead to undesired bridging of the drill hole.

Another factor to consider when using nodules of bentonite to plug awell is the salinity of any water in the well. In many cases salinitywill not be a limitation but if the water is highly saline, in somecases the nodules may exfoliate and break up. The hydration still takesplace but the nodules have been granulated and the plug produced willlikely have less density and therefore higher permeability than desiredfor the purpose of well plugging. This problem can be solved fordifferent salinities by varying the water saturation in the nodulesthemselves, by slightly pre-hydrating the nodules prior to wellplacement or alternatively by diluting the salinity of the water in thewell bore during placement of the nodules. Compacted nodules of thisinvention were tested at three levels of salinity—fresh water, sea water(19,000–23,000 mg/L chlorides) and saturated brine (189,000 mg/Lchlorides). The compacted nodules exhibited markedly differentcharacteristics than are typically observed with noncompacted materials.Compacted nodules containing about 16% by weight nonconnate water gavegood results and exhibited only minor exfoliation and break down.

In all cases, the bentonite nodules swell when contacted with additionalwater and form a hydraulically solid plug of expanded bentonitecontaining about 38% by weight water.

EXAMPLES

The invention will be further illustrated by the following examples.These are provided to demonstrate the practice of this invention and arenot to be construed as limitations on the invention which is defined bythe claims. The examples were conducted and recorded in a format usedpreviously for briquet making. The report description therefore at timeslabels the nodules as “briquets”. Some of the data were recorded ininternational system of units while other data were recorded in Englishunits. Conversions between these units can be carried out using factorstaken from the following conversion table.

CONVERSION TABLE INTERNATIONAL SYSTEM OF UNITS (SI) TO ENGLISH UNITS 1[mm] 0.03937 [in] 1 [g/cm^(3]) 62.42000 [lb/ft^(3]) 1 [t] 2,204.60000[lb] 1 [t/h] 2,204.60000 [lb/h] 1 [N] 0.22480 [lb] 1 [MN] 224,809.00000[lb] 1 [MN/m] 5,710.16000 [lb/in] 1 [MPa] 145.03800 [PSI] 1 [kW] 1.34100[HP]

Example 1

K. R. Komarek model B100R, B220QC and B400A roller presses were used inall trials. FIG. 4 shows schematically the cross section of thesemachines. Feedstock material from the feed hopper was supplied into theroll nip with a horizontal screw, driven by a variable speed drive unit.A paddle mixer was utilized to agitate feedstock material into thehorizontal screw at the feed inlet.

The material was then compacted between two rolls which are cantileveredon the ends of shafts outside the bearing blocks. A fully adjustablehydraulic system provides the force holding the rolls together. Thisforce is equal in magnitude to the roll-separating force generated bythe compacted material in the roll nip. A gas-filled accumulator in thehydraulic system acts as a pressured reservoir. Accumulator pre-chargepressure determines the hydraulic system stiffness.

Feedstocks described in Table 1, made up of bentonite with various watercontents, were placed into the feed hopper. The roll-pressing processwas then tested. After the roll press was operating under stableconditions, all the data were collected. These data presented in Table2. The properties of the nodules produced in the tests are listed inTable 3.

Two methods were used to compare nodule strength:

A. Crushing Strength.

The nodule was placed between two parallel plates and loaded untilfailure. Nodule strength is expressed as the maximum force the noduleresists before failing.

B. Drop Strength.

The nodule was dropped on the concrete floor. Drop strength was definedas the height of drop at which more than 50% of nodules start to breakbecause of impact. If the drop strength was over 2.0 m, the number ofdrops from 2.0 m was additionally recorded.

The nodules were flattened spheres shaped as shown in FIG. 3 withDM=2.97″ and Dm=1.5″.

As can be seen from the product data given in Table 3, the nodules arecompacted and durable.

Example 2

A series of nodule preparation runs were conducted on a Komarek B 400Broll press machine. The nodule size was 2¾ inches by 1¾ inches.

The roll clearance was 0.060″. A variety of bentonite feedstocks varyingin water content was employed.

One first set of 9 runs was made with dry bentonite (essentially noadded water).

The initial run was made with the hydraulic pressure set at 1100 psi andthe rolls and feed screw run at 58 RPM and 25 RPM, respectively. Theindicated pressure shot up beyond 2000 psi. The action appeared to bestiff.

Another initial run was made with the feed screw slowed down to 15 RPM.This was done in case the 1100 psi machine setting was sufficient. Inboth initial runs, nodules were formed, although they were unacceptableas they were being crushed and split during production.

Because of these results, the hydraulic pressure was decreased to 700psi, the roll was kept at a full 60 RPM and the feed screw slowed downto 10 RPM. Nodules were produced at first, but they were not well formedand still appeared to be crushed and brittle.

Run 2 was performed with the roll drive at a full capacity of 60 RPM.The feed screw was run at 13 RPM but the nodule quality did notsignificantly improve.

Feed screw speed was slowed to 11 RPM and the roll speed slowed to 58RPM as well. Hydraulic pressure was set to 600 psi. Nodule quality wasslightly better.

In the next run, the pressure was increased to 700 psi with all otherconditions being the same. The needle on the gauge showed a morecontrolled response, and the nodule quality was the best thus far,although not particularly strong.

In order to determine the range of pressure under different conditions,the next run was done at 850 psi with the same roll speed and a slightlyfaster feed screw (13 RPM). The machine became very sensitive. Thus, thenext run was made with the same conditions but with the pressure droppedto 600 psi. The nodule quality was improved.

Another run was made to determine the bottom range of the feed screw ata lower pressure. At 500 psi, with the feed screw at 11 RPM and therolls at 58 RPM, quality nodules were made. They were slightly roughabout the edges, but otherwise they were aligned.

Run 8 was done in the same way with the rolls run at maximum. Thenodules were as good as in the previous run.

Given the above data, it appears that the optimal pressure range for themachine is between 500 and 600 psi. 700 psi is possible. The rolls canbe run as high as 58–60 RPM under these conditions, but the feed screwmust be run at a slow 11 RPM with a maximum of 13 RPM before the machinebecomes very sensitive.

Just to re-verify the pressure, a small run was done from with theoptimal feed and roll speeds but at 400 psi pressure. The nodules werestill of good quality, but not as good as the runs that determined theoptimal conditions.

Hence, when the conditions are optimal, the nodules are very strong, ofexcellent quality, and the needle on the hydraulic pressure shows veryslight deviations from its set pressure indicating a good spring effect.

Further runs were performed in order to fully exploit the range ofquality nodules. The previous nodule, particularly of run 5 at 0%moisture, was a good nodule, so it was to be determined if a higherquality nodule was possible.

In the next series of runs, the feedstock was changed. A bentonitematerial of 7% moisture was used. The bentonite with this added moistureshowed improved roll pressing. It was also found that the material waseasily briquetted in general, requiring less hydraulic pressure thanwith dry material. In order to verify this, the pressure was kept at300–400 psi for each run. The response in the pressure readings was muchmore favorable than had previously been observed. In addition, thenodules were showing improved quality, with excellent strength. Almostall nodules survived 2 meter drop tests, and a good number surviveddrops of as much as 5 meters.

Though these nodules were quite good, there still seemed to be a lot ofsensitivity in the hydraulic pressure responses in the roll pressing,and when the 7% moisture material was depleted, 14% moisture feedstockmaterial was used to focus on the pressure response and motor speeds.

With 14% moisture content, it was seen that the nodules showed immediateimprovements in roll pressing from just the moisture alone. The moisturecontent of 14% seemed to be quite ideal. For the first few runs, thepressure was lowered to 300 psi in an attempt to improve the surfacequality by eliminating cracks and clam shelling from too high pressures,and the motors were run to compensate and improve strength. The third14% moisture run showed a well-developed nodule.

A continuous, steady production run was also sought. The next few runswere made not only to meet these objectives, but to get a betterdetermination as to the range of speeds available. A lower pressure wasfound to work quite well, and this is beneficial as it extends the rolllife of the machine. Fuller nodules were made with the correct feed ofmaterial from the feed screw. The rolls had the most range of operationavailable to them, being able to run in a bit slower, or even at fullcapacity.

With each run, the nodules would improve but the belts were apt to slip.After correcting with the pressure and the feed screw speed, the optimalrunning conditions were narrowed down and locked into a specific range.The nodules had improved so much that they were of the utmost instrength, quality and appearance for this size. This good productquality was present during a continual and lengthy run.

The results for all of the above trials are in Table 4. It has beenshown that the higher amount of moisture (14%) is very beneficial tohigh quality manufacturing. Best results were obtained with thefollowing conditions.

-   -   With 14% moisture:    -   Hydraulic pressure: 250 psi    -   Roll Cycles/Load: 58–60 RPM    -   Screw cycles/Load: 12–13 RPM    -   With 7% moisture:    -   Hydraulic pressure: 300 psi    -   Roll Cycles/Load: 52–54 RPM    -   Screw cycles/Load: 11 RPM    -   With 0% moisture:    -   Hydraulic pressure: 500–600 psi    -   Roll Cycles/Load: 58–60 RPM    -   Screw cycles/Load: 11 RPM        -   (If material flow is good and consistent from the feed            inlet, 700 psi and 13 RPM on the screw is possible.)

Example 3

The nodules formed as a result of the knowledge gained from Examples 1and 2 were evaluated in the laboratory and in the field.

Laboratory Tests

Test No. 1

The effect of salinity on compressed bentonite nodules' ability to forma hydraulically solid plug was evaluated. Nodules containing about 16%by weight nonconnate water were used.

Test Methodology: Freshwater

Nodules were placed in a mason jar, covered with freshwater, and the jarwas closed with a lid. On visual inspection, within 12 hours the noduleshad hydrated to form a solid plug and consumed the water in the jar.

Test Methodology: Seawater

A sample of Gulf of Mexico seawater (19,000–23,000 mg/L chlorides) wasused. Nodules were placed in a jar, covered with seawater, and the jarwas closed. Within a few minutes some of the bentonite was observedflaking off of the nodules. Twelve hours later, the nodules had formed ahydraulically solid plug and consumed the water in the jar.

Test Methodology: Saturated Sodium Chloride

A sample of saturated sodium chloride brine (189,000 mg/L chlorides) wasused in the same test. Within a few minutes, some of the bentonite wasobserved flaking off of the nodules. Twelve hours later, the nodules hadformed a hydraulically solid plug and consumed the water in the jar.

This showed that in most cases there may be no salinity limit on theability of compressed sodium bentonite nodules to form a hydraulicallysolid plug. However, extremely high salinity levels may lead to somedesiccation and exfoliation of the bentonite nodules. This can occur asthe nodules fall through a layer of extremely saline water.

Test No. 2

This test was to determine what happens to a compressed sodium bentonitenodule-based plug that has been hydrated in freshwater and then isplaced in a saline water environment.

Test Methodology: Saltwater Bath of Freshwater Plug

A wire mesh container for the nodules was fashioned to allow forobservation of the plug from all sides. Nodules were placed in thecontainer and immersed in freshwater and allowed to hydrate overnight. Asolution of saturated salt water (189,000 ppm chlorides) was prepared.The wire mesh container was removed from the freshwater and immersed inthe saltwater bath. The salinity of the saltwater solution wasperiodically measured based on its conductivity. Although initiallythere was a slight decrease in conductivity of the saltwater, thesalinity recovered and stabilized. The plug continued to hydrate. Noshrinkage was observed, and no deterioration of the plug was observed.The test ran for over 60 days.

This test shows that desiccation does not take place in a presaturatedfresh water condition.

Test No. 3

The test was to determine whether the nodules will be washed away bywater running through an unhydrated plug.

Test Methodology: Bentonite Washout

A clear plastic container with holes in the bottom was filled withcompressed bentonite nodules. Water was continuously run through thecontainer. The run-off solution was inspected of bentonite particles.Within 3 hours, the bentonite had hydrated sufficiently to retard theflow to negligible amounts. The container became deformed due to theswelling of the nodules as they hydrated. There was a minor clouding ofthe water utilized for the experiment. This indicated that washout wouldnot be a problem.

Test No. 4

A test was conducted to determine whether an oil coating and an oilywater environment would inhibit hydration of the compressed bentonitenodule.

Test Methodology: Hydration in Oily Environments

A jar was filled with oily produced water, 19° API, with a free oillayer that was thicker than one nodule. Nodules were individuallydropped through the oil layer into the jar. Twelve hours later thenodules had formed a hydraulically solid plug. The only liquid remainingin the jar was free oil. All of the water was consumed by the nodules.The presence of oil or oil coating of the nodule did not affect thehydration rate since there was access to water.

Test No. 5

The effect of steam flow created prior to complete hydration of acompressed sodium bentonite plug was studied to determine if the steamwill prevent sealing of the open flow paths.

Test Methodology: Hydration in Steam Environments

A mason jar was layered with pea gravel, bentonite nodules and more peagravel. 200° F. freshwater was placed in the jar. The jar was heated,producing boiling water and steam escaping through a preferential flowpath. Within two hours, the open flow paths were observed to have sealeddue to hydration of the bentonite. The experiment was suspended. Thetest jar was set aside. Two days later, observation of the jar suggestedthat swelling pressure had broken the jar, but the gravel and thebentonite had formed a solid plug. The steam and boiling agitation haddistributed bentonite particles throughout the gravel pore spaces.Preferential flow paths did not remain open during the experiment due tohydration.

Test No. 6

The effect of hydrogen sulfide on bentonite hydration was examined.

Test Methodology: Hydration in H₂S Environment

A nodule was immersed in a jar of freshwater while at the same timeanother nodule was placed in a jar of saturated hydrogen sulfide water.Both nodules hydrated. By visual inspection, the nodule in the hydrogensulfide water swelled about 70 percent as much as the nodule infreshwater. This showed that bentonite will hydrate in saturatedhydrogen sulfide water. However, bentonite swelling capacity appears tobe affected by the presence of H₂S.

Field Tests

Three generalized drill hole plugging designs were tested. The threedesigns were dependent upon the presence of freshwater and thecalculated top of cement. The principle utilized in the design was torestore well bore flowpaths to their preexisting states. In short, whereclay once resided, place clay; where porous and permeable formationsexist, place like material, including intervals across perforations.This, in effect, would return the material from whence it came. As willbe described below, the plug was to be 110 feet in total length.

FIG. 5 depicts the three design schematics.

Case 1—No Freshwater Present

As shown in FIG. 5A, a plugged well 20 is made up of a cement wellcasing 22 extending from the topmost perforation 24 of producing zone 26to the surface 28. Alternatively, the well casing 22 could extend from awater shut off or from a linear top (whatever is highest) to the surface28.

This plugging called for the isolation of the producing zone 26 from thesurface through the placement of a 110 ft. zonal plug 30. In addition tothe zonal plug, a 25 ft. surface plug 32 was placed.

To ensure that the bentonite plug 30 provided an effective seal aroundthe liner top, it was decided to extend the bottom of the zonal plug 30by ten feet, penetrating the liner, if present, and, at times, reachingbelow the topmost perforations or water shut-off. This ten footextension is identified as 34. Using the same logic, the surface plugwas also extended an additional twenty-five feet as shown at 36 toensure isolation.

The space between plugs 30 and 32 was filled with gravel 38.

Of the nineteen wells plugged in the field test, eleven were of the Case1 design.

Case 2—Freshwater Present. Cement in Annulus Above Freshwater Interface

As shown in plugged well 40 in FIG. 5B, when freshwater is present, suchas at level 42, an operator is required to protect it from potentialcontamination from both the producing zone 26 and the surface 28.Although the annulus at and near the freshwater interface 42 isprotected from corrosive formation waters by a sheath of cement 22, in aCase 2 well, should the integrity of this sheath fail, the potential forfreshwater contamination is great. Therefore, in addition to theproducing zone plug 30 and the surface plug 32, an operator is alsorequired to place a 100 ft. plug 44 across the freshwater interface 42.By design, this plug should effectively shut off the possibility forcommunication from both above and below. Gravel fills regions 38 and 46.

There were four pilot wells of the Case 2 design which were plugged.

Case 3—Freshwater Present. Cement Top in Annulus Below FreshwaterInterface

As shown in FIG. 5C, the bentonite nodules can also be used to plugwells such as well 60 where the concrete annulus 22 does not extend allthe way to the surface 28 and in which freshwater 42 may be found in theregion between the top of the concrete annulus and the surface. In thiscase, producing plug 38 and surface plug 32 are substantially as shownin FIGS. 5A and 5B.

It was proposed to fire a cavity shot at the base of freshwater 42, andsubsequently fill the hole and cavity 46 created by the cavity shot withbentonite nodules. Cavity shots are currently the required method whenmore than one string of casing is present at the base of freshwater.

The abandonment would be completed in two phases, the initial producingzone plug 30, then the cavity shot (with a rat-hole providing for theencasing of debris within bentonite) and the freshwater plug 46 and thesurface plug 32.

There were four wells plugged utilizing the cavity shot technique (Case3).

Field Results

Plugging of nineteen wells within a Coalinga, California oil field wascompleted utilizing compressed, preformed bentonite nodules, which serveas a permanent clay barrier to fluid migration within the well bore. Thefollowing section details the execution at the field level, and theresults obtained. The results are summarized in Table 5, as well.

Implementation

Bentonite nodules were to be used in lieu of cement, with gravel used asfill material. One of the benefits of the bentonite process overconventional cement abandonments is the lack of need for customarycement pump trucks, coiled tubing units and bulk cement units. In orderto accomplish the objectives, the pilot wells were divided into twodiscrete subsets: the first ten wells where placement success wasconsidered the highest objective; and the second nine wells where thefocus was directed towards process efficiency. The results of thepluggings are summarized below and in the Table 5.

Pilot Learnings

Nineteen wells in the Coalinga Oil Field were plugged using compressedbentonite nodules. Eleven of the wells were of the Case 1 design, whilethe remaining eight were equally split between Case 2 and Case 3.

The densely compacted bentonite nodules fell through the first ten wellsattempted (predominantly primary producers) without incident. Thebentonite was placed into the wells utilizing a chute and funnel at arate of about one forty pound box per minute. The bottom plug 30 wastypically placed by pouring the bentonite dry, without the presence ofwater, from surface and allowing it to hit the air/liquid interface,which was approximately 1,000 feet below ground level. The nodulesconsistently penetrated the interface without bridging and fell throughthe liquid column to the desired depth.

Upon witnessing the placement of the plug 30, water was then added, ifneeded, to hydrate the plug. It should be noted that proper plughydration was ensured and verified through the sampling of formationliquids prior to material placement to ascertain adequate water cuts,and the sustained presence of standing water upon execution ofsubsequent stages within a given well's abandonment.

Pea gravel and larger sized gravel (¾″-minus) 38 was used in the pilot.The larger sized gravel was preferred as it more closely approximatedthe size and density of the bentonite nodules.

The temperature and timing of water placed in the well also variedduring the plugging of the first ten wells. This had a pronounced effecton bridging, as is discussed below.

Subset No. 1: First Ten Wells

Two means of placing bentonite and gravel were explored during theplugging of the first ten wells: dry pouring, and pouring into a columnof liquid. Initially, material was poured into the well and water addedafter the proper bentonite depth was verified. Since the pea gravel andthe ¾″-minus gravel both were observed to bridge occasionally whilefree-falling several hundred feet to the air/liquid interface, it wasdecided to fill the entire well bore with water to minimize theseevents. This did result in the elimination of gravel bridging, but alsodecreased the application rate at the surface, and increased thesettling time downhole considerably. There was, however, a netimprovement when considering the downtime caused by bridging.

In addition, the temperature of the hydrating water was also varied inan attempt to reduce the viscosity of the heavy oil, especially at thefluid interface. The combined effect of wellborn fill-up, with hot water(approximately 130° F.), a process derived by the end of the first tenwells, appeared to have solved the placement and bridging issues.

The addition of hot produced water preceding the introduction ofabandonment materials and between the alternating stages of bentoniteand gravel also improved efficiency by reducing the number of gravelbridge-offs.

Subset No. 2: Last Nine Wells

The focus of the last nine wells was to improve the placement rate ofgravel and bentonite nodules. The first ten wells identified a need forwater during gravel placement, coupled with the realization that hotwater would reduce the fluid viscosity at the interface. Therefore, itwas decided to fill the wells partially with hot water upon thecommencement of abandonment work. Prior to adding gravel and bentonite,the wells were treated with a minimum of one casing volume of hot water.

This modification resulted in the elimination of gravel bridging.Unfortunately, after placing the first bentonite plug, the slicklineunit indicated that the bentonite had bridged high. This was the firstoccasion in which the bentonite had not fallen to its intended depthwithout incident. Unsure of the cause, and suspecting somecharacteristic particular to this well alone (perhaps the higher gravitycrude oil present), the operations crew proceeded to bridge twoadditional wells with bentonite utilizing the same new technique, hotwater with bentonite.

It was at this time that the effects of heat on bentonite hydration werefully understood at the field level. Prior use of hot water in the firstten wells was used after placing bentonite and before pouring gravel.Now, hot water was constantly being added to the well with noopportunity for downhole cooling to occur prior to the addition ofbentonite.

The predicament for operations was the need for hot water to assist inviscosity reduction for the gravel's sake, and the need for cool waterto ensure effective placement of bentonite. The solution obtained was toallow the bentonite to free-fall as much as possible in the well bore toreduce settling time and achieve a high confidence level of it reachingits objective depth. Once there, and verified with a slickline tag, hotwater could be trickled into the well while gravel was poured. The waterthen served to hydrate the bentonite and prevent gravel bridges.

As a further means of optimization, the trickling of the hot water intothe well was stopped prior to the end of the gravel stage. This servedto cool the water before the introduction of bentonite.

The modified placement technique made for an efficient and effectiveplug. In every case, the bottom plug hydrated fully, as evidenced bystanding columns of fluid at the surface before the plugging was evencompleted. As a result, subsurface plugging time was reduced.

Additionally, a core was taken of the surface plug of a well for thepurpose of obtaining its permeability. The core was taken at a depth ofapproximately eleven feet from the surface after the conductor andsurface casing were cut-off. Upon removing the casing, a hydraulicallysolid plug was exposed from which the core sample was obtained. Testsindicated that the plug had an air permeability of less than 0.1 (lessthan the lowest measurement the apparatus can obtain), a waterpermeability of 0.0014 and a hydraulic conductivity of 1.44×10-9 cm/s.

TABLE NO. 1 FEED MATERIAL PROPERTIES DATA SHEET - BATCH 1. CHEMICAL NAMEBENTONITE MOLECULAR FORMULA SAMPLE MARKED “BH#4” MOISTURE CONTENT % 18.5TRUE DENSITY g/cm³ BULK DENSITY (LOOSE) g/cm³  1.11 BULK DENSITY(PACKED) g/cm³  1.24 HARDINESS MOHS SCALE ANGLE OF REPOSE deg NOTMEASURED ANGLE OF FALL deg ANGLE OF DIFFERENCE deg OTHER MATERIALRETAINED ON SIEVE MASS MASS MESH MICRONS MASS g FRACTION % ACCUMUL %  82380 7.4 2.7 2.7  18 1000 63.2 23.5 26.2  35 500 68.1 25.3 51.5  70 21062.4 23.2 74.7 140 105 39.2 14.6 89.2 200 74 14.1 5.2 94.5 325 44 0.70.3 94.7 PAN #N/A 14.2 5.3 100.0 FEED MATERIAL PROPERTIES DATA SHEET -BATCH 2. CHEMICAL NAME BENTONITE MOLECULAR FORMULA SAMPLE MARKED “12–40”MOISTURE CONTENT % 10.2 TRUE DENSITY g/cm³ BULK DENSITY (LOOSE) g/cm³ 1.09 BULK DENSITY (PACKED) g/cm³  1.18 HARDINESS MOHS SCALE ANGLE OFREPOSE deg NOT MEASURED ANGLE OF FALL deg ANGLE OF DIFFERENCE deg OTHERMATERIAL RETAINED ON SIEVE MASS MASS MESH MICRONS MASS g FRACTION %ACCUMUL %  8 2380 5.2 1.7 1.7  18 1000 110.8 36.0 37.7  35 500 135.443.9 81.6  70 210 55.8 18.1 99.7 140 105 0.4 0.1 99.8 200 74 0.2 0.199.9 325 44 0 0.0 99.9 PAN #N/A 0.3 0.1 100.0 FEED MATERIAL PROPERTIESDATA SHEET - BATCH 3. CHEMICAL NAME BENTONITE MOLECULAR FORMULA SAMPLEMARKED “GRAN. FINES” MOISTURE CONTENT % 9.1 TRUE DENSITY g/cm³ BULKDENSITY (LOOSE) g/cm³ 1.16 BULK DENSITY (PACKED) g/cm³ 1.28 HARDINESSMOHS SCALE ANGLE OF REPOSE deg NOT MEASURED ANGLE OF FALL deg ANGLE OFDIFFERENCE deg OTHER MATERIAL RETAINED ON SIEVE MASS MASS MESH MICRONSMASS g FRACTION % ACCUMUL %  8 2380 0.4 0.1 0.1  18 1000 1.5 0.5 0.6  35500 3.8 1.2 1.7  70 210 151.0 45.8 47.6 140 105 84.5 25.6 73.2 200 7426.3 8.0 81.2 325 44 27.1 8.2 89.4 PAN #N/A 34.9 10.6 100.0 FEEDMATERIAL PROPERTIES DATA SHEET - BATCH 4. CHEMICAL NAME BENTONITEMOLECULAR FORMULA SAMPLE MARKED - LAST SHIPMENT MOISTURE CONTENT % 20.2TRUE DENSITY g/cm³ BULK DENSITY (LOOSE) g/cm³  1.03 BULK DENSITY(PACKED) g/cm³  1.16 HARDINESS MOHS SCALE ANGLE OF REPOSE deg NOTMEASURED ANGLE OF FALL deg ANGLE OF DIFFERENCE deg OTHER MATERIALRETAINED ON SIEVE MASS MASS MESH MICRONS MASS g FRACTION % ACCUMUL %  82380 35.2 9.1 9.1  18 1000 48.5 12.5 21.7  35 500 82.3 21.3 42.9  70 210159.1 41.2 84.1 140 105 33.9 8.8 92.9 200 74 24.5 6.3 99.2 325 44 0.90.2 99.5 PAN #N/A 2.1 0.5 100.0

TABLE NO. 2 Roll Press Set Up, Test Conditions and ProcessCharacteristics RUN NO. RUN NO. RUN NO. RUN NO. RUN NO. RUN NO. RUN NO.RUN NO. 1 2 3 4 5 6 7 8 TESTED MATERIAL BATCH 1 BATCH 1 BATCH 1 BATCH 1BATCH 1 BATCH 2 BATCH 2 BATCH 2 FEED MATERIAL BULK DENSITY g/cm³ 1.111.11 1.11 1.11 1.11 1.09 1.09 1.09 MACHINE MODEL B-220QC B-220QC B-220QCB-220QC B-220QC B-220QC B-220QC B-220QC ROLLS PART NO. B2487 B2487 B2487B2487 B2487 B2487 B2487 B2487 ROLL DIAMETER mm 305 305 305 305 305 305305 305 NO. OF POCKETS (CORRUGATIONS) 24 24 24 24 24 24 24 24 NO. OFROWS 1 1 1 1 1 1 1 1 ROLL FACE WIDTH mm 76 76 76 76 76 76 76 76 ROLLSPEED rev/min 3.0 3.0 3.0 3.0 14.7 12.4 3.0 3.0 ROLL TORQUE Nm 3672 38153037 2736 2689 2915 3029 3910 ROLL DRIVE POWER INDEX kW 1.16 1.20 0.960.86 4.15 3.80 0.95 1.23 FEED SCREW PART NO. FEED SCREW OUTSIDE DIA mm73 63 63 63 63 63 63 63 FEED SCREW ROOT DIA mm 41 35 35 35 35 35 35 35FEED SCREW PITCH mm 51 51 51 51 51 51 51 51 SCREW BARREL INSIDE DIA mm76 76 76 76 76 76 76 76 FEEDSCREWSPEED rev/min 31 58 52 49 391 391 82 91SCREW TORQUE Nm 284 158 123 115 78.5 45 43 53 FEED SCREW DRIVE POWER INDkW 0.92 0.96 0.67 0.59 3.22 1.85 0.37 0.51 PRESSURE IN HYDRAULIC SYS MPaINITIAL ACCUMULATOR PRESSURE MPa 6.89 6.89 6.89 6.89 6.89 6.89 6.89 6.89ROLL SEPARATING FORCE MN 0.184 0.187 0.122 0.069 0.057 0.096 0.105 0.141INITIAL ROLL GAP mm 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 WEB THICKNESS mm 0.70.9 1.2 2.3 2.9 3.1 2.6 2.1 BRIQUET CALCULATED PRESSURE MPa 60.64 61.6340.21 22.74 18.79 31.64 34.60 46.47 RATIO OF TANGENTIAL TO RADIAL STRESS0.13 0.13 0.16 0.26 0.31 0.20 0.19 0.18 MEASURED THROUGHPUT t/h 0.26420.2609 0.2731 0.2945 1.5382 1.3472 0.3127 0.3207 BRIQUET TEMPERATUREDEG.C NOT NOT NOT NOT NOT NOT NOT NOT MEAS MEAS MEAS MEAS MEAS MEAS MEASMEAS BRIQUET WEIGHT g 57.91 57.61 59.48 63.51 66.25 67.52 66.45 69.65BRIQUET NET PRODUCTION RATE t/h 0.2502 0.2489 0.2570 0.2744 1.40241.2056 0.2871 0.3009 FINES PERCENTAGE % 5.3 4.6 5.9 6.8 8.8 10.5 8.2 6.2FEED SCREW EFFICIENCY % 87.6 61.5 71.7 82.1 53.7 47.2 53.1 49.0 ROLLDRIVE ENERGY CONS. kWh/t 4.4 4.6 3.5 2.9 2.7 2.8 3.1 3.8 SCREW DRIVEENERGY CONS. kWh/t 3.5 3.7 2.5 2.0 2.1 1.4 1.2 1.6 RUN NO. RUN NO. RUNNO. RUN NO. RUN NO. RUN NO. RUN NO. RUN NO. 9 10 11 12 13 14 15 16TESTED MATERIAL BATCH 2 BATCH 3 BATCH 3 BATCH 3 BATCH 3 BATCH 4 BATCH 4BATCH 4 FEED MATERIAL BULK DENSITY g/cm³ 1.09 1.16 1.16 1.16 1.16 1.031.03 1.03 MACHINE MODEL B-220QC B-220QC B-220QC B-220QC B-220QC B-220QCB-220QC B-220QC ROLLS PART NO. B2487 B2487 B2487 B2487 B2487 B2487 B2487B2487 ROLL DIAMETER mm 305 305 305 305 305 305 305 305 NO. OF POCKETS(CORRUGATIONS) 24 24 24 24 24 24 24 24 NO. OF ROWS 1 1 1 1 1 1 1 1 ROLLFACE WIDTH mm 76 76 76 76 76 76 76 76 ROLL SPEED rev/min 3.0 3.0 3.0 3.016.4 3.0 3.0 3.0 ROLL TORQUE Nm 5036 5108 3997 2982 4095 2895 2490 2162ROLL DRIVE POWER INDEX kW 1.59 1.61 1.26 0.94 7.05 0.91 0.78 0.68 FEEDSCREW PART NO. FEED SCREW OUTSIDE DIA mm 63 63 73 63 63 63 63 63 FEEDSCREW ROOT DIA mm 35 35 41 35 35 35 35 35 FEED SCREW PITCH mm 51 51 5151 51 51 51 51 SCREW BARREL INSIDE DIA mm 76 76 76 76 76 76 76 76FEEDSCREWSPEED rev/min 94 71 69 82 391 67 66 66 SCREW TORQUE Nm 72 12993 43 67 228 148 76 FEED SCREW DRIVE POWER IND kW 0.71 0.96 0.67 0.372.75 1.60 1.03 0.53 PRESSURE IN HYDRAULIC SYS MPa INITIAL ACCUMULATORPRESSURE MPa 6.89 6.89 6.89 6.89 6.89 6.89 6.89 6.89 ROLL SEPARATINGFORCE MN 0.202 0.205 0.148 0.086 0.153 0.185 0.141 0.084 INITIAL ROLLGAP mm 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 WEB THICKNESS mm 2.0 2.1 2.2 3.12.4 0.7 0.7 0.8 BRIQUET CALCULATED PRESSURE MPa 66.57 67.56 48.78 28.3450.42 60.97 46.47 27.68 RATIO OF TANGENTIAL TO RADIAL STRESS 0.16 0.160.18 0.23 0.18 0.10 0.12 0.17 MEASURED THROUGHPUT t/h 0.3253 0.32310.3061 0.3247 1.7124 0.2571 0.2592 0.2641 BRIQUET TEMPERATURE DEG.C NOTNOT NOT NOT NOT NOT NOT NOT MEAS MEAS MEAS MEAS MEAS MEAS MEAS MEASBRIQUET WEIGHT g 70.51 69.82 66.85 70.50 66.15 56.85 56.72 57.95 BRIQUETNET PRODUCTION RATE t/h 0.3046 0.3016 0.2888 0.3046 1.5622 0.2456 0.24500.2503 FINES PERCENTAGE % 6.4 6.6 5.7 6.2 8.8 4.5 5.5 5.2 FEED SCREWEFFICIENCY % 48.1 59.5 50.1 51.8 57.2 56.5 57.8 58.9 ROLL DRIVE ENERGYCONS. kWh/t 4.9 5.0 4.1 2.9 4.1 3.5 3.0 2.6 SCREW DRIVE ENERGY CONS.kWh/t 2.2 3.0 2.2 1.1 1.6 6.2 4.0 2.0 RUN NO. RUN NO. RUN NO. RUN NO. 1718 19 20 TESTED MATERIAL BATCH 4 BATCH 4 BATCH 1 BATCH 2 FEED MATERIALBULK DENSITY g/cm³ 1.03 1.03 1.11 1.09 MACHINE MODEL B-220QC B-100RB-400A B-400A ROLLS PART NO. B2487 B1116-4 B4609 B4609 ROLL DIAMETER mm305 130 460 460 NO. OF POCKETS (CORRUGATIONS) 24 18 22 22 NO. OF ROWS 12 2 2 ROLL FACE WIDTH mm 76 51 152 152 ROLL SPEED rev/min 15.1 3.0 2.42.4 ROLL TORQUE Nm 2308 520 10800 18500 ROLL DRIVE POWER INDEX kW 3.660.16 2.72 4.66 FEED SCREW PART NO. B180-9 B469 B469 FEED SCREW OUTSIDEDIA mm 63 44 140 140 FEED SCREW ROOT DIA mm 35 19 95 95 FEED SCREW PITCHmm 51 40 76 76 SCREW BARREL INSIDE DIA mm 76 51 148 148 FEEDSCREWSPEEDrev/min 391 57 48 73 SCREW TORQUE Nm 65 79 420 285 FEED SCREW DRIVEPOWER IND kW 2.67 0.47 2.12 2.49 PRESSURE IN HYDRAULIC SYS MPa INITIALACCUMULATOR PRESSURE MPa 6.89 6.89 6.89 6.89 ROLL SEPARATING FORCE MN0.086 0.054 0.210 0.399 INITIAL ROLL GAP mm 0.4 0.6 1.0 1.0 WEBTHICKNESS mm 0.9 0.7 1.2 3.3 BRIQUET CALCULATED PRESSURE MPa 28.34 46.6721.03 39.96 RATIO OF TANGENTIAL TO RADIAL STRESS 0.18 0.15 0.22 0.20MEASURED THROUGHPUT t/h 1.3247 0.0432 1.0215 1.1805 BRIQUET TEMPERATUREDEG.C NOT NOT NOT NOT MEAS MEAS MEAS MEAS BRIQUET WEIGHT g 57.45 6.15161.22 186.31 BRIQUET NET PRODUCTION RATE t/h 1.2492 0.0399 1.02151.1805 FINES PERCENTAGE % 5.7 7.7 NOT NOT MEAS MEAS FEED SCREWEFFICIENCY % 49.9 24.8 50.6 39.2 ROLL DRIVE ENERGY CONS. kWh/t 2.8 3.82.7 3.9 SCREW DRIVE ENERGY CONS. kWh/t 2.0 10.9 2.1 1.8

TABLE 3 Product Evaluation RUN NO. 1 RUN NO. 2 RUN NO. 3 RUN NO. 4 RUNNO. 5 RUN NO. 6 BRIQUETWEIGHT g 57.54 57.43 58.46 65.45 66.52 68.72BRIQUETVOLUME cm3 27.27 27.22 27.84 31.32 31.98 32.72 BRIQUETDENSITYg/cm3 2.11 2.11 2.10 2.09 2.08 2.10 BRIQUETS BULK DENSITY t/m3 NOT MEAS.NOT MEAS. NOT MEAS. NOT MEAS. NOT MEAS. NOT MEAS. BRIQUETS “GREEN”STRENGTH MEAN CRUSHING FORCE N 1325.5 1227.6 1245.4 1316.6 1076.4 1797.1DROP HEIGHT AT FAILURE m 2.0 2.0 2.0 2.0 2.0 1.8 NUMBER OF DROPS 6 6 178 10 1 RUN NO. 7 RUN NO. 8 RUN NO. 9 RUN NO. 10 RUN NO. 11 RUN NO. 12BRIQUETWEIGHT g 65.01 70.37 70.52 70.29 66.59 70.28 BRIQUETVOLUME cm330.81 32.28 32.05 32.09 30.83 33.31 BRIQUETDENSITY g/cm3 2.11 2.18 2.202.19 2.16 2.11 BRIQUETS BULK DENSITY t/m3 NOT MEAS. NOT MEAS. NOT MEAS.NOT MEAS. NOT MEAS. NOT MEAS. BRIQUETS “GREEN” STRENGTH MEAN CRUSHINGFORCE N 1556.8 1859.3 2143.9 2215.1 >2224 1663.5 DROP HEIGHT AT FAILUREm 1.5 1.2 2.0 1.8 2.0 1.2 NUMBER OF DROPS 1 1 2 1 2 1 RUN NO. 13 RUN NO.14 RUN NO. 15 RUN NO. 16 RUN NO. 17 RUN NO. 18 BRIQUETWEIGHT g 66.0255.48 56.79 57.61 57.66 6.14 BRIQUETVOLUME cm3 30.85 25.93 26.41 26.9226.94 2.84 BRIQUETDENSITY g/cm3 2.14 2.14 2.15 2.14 2.14 2.16 BRIQUETSBULK DENSITY t/m3 NOT MEAS. NOT MEAS. NOT MEAS. NOT MEAS. NOT MEAS. NOTMEAS. BRIQUETS “GREEN” STRENGTH MEAN CRUSHING FORCE N 2046.1 1192.01227.6 1120.9 1014.2 427.1 DROP HEIGHT AT FAILURE m 1.2 2.0 2.0 2.0 2.02.0 NUMBER OF DROPS 1 >20 >20 >20 >20 >20 RUN NO. 19 RUN NO. 20BRIQUETWEIGHT g 161.22 186.31 BRIQUETVOLUME cm3 NOT MEAS. NOT MEAS.BRIQUETDENSITY g/cm3 NOT MEAS. NOT MEAS. BRIQUETS BULK DENSITY t/m3 NOTMEAS. NOT MEAS. BRIQUETS “GREEN” STRENGTH MEAN CRUSHING FORCE N 1147.61912.6 DROP HEIGHT AT FAILURE m 2.0 1.5 NUMBER OF DROPS 6 1

TABLE 4 ROLL HYDRAULIC CYCLES/ SCREW PRESSURE LOAD CYLCES/ (psi) (Hz/A)LOAD Hz/A) RESULTS MATERIAL: BENTONITE @0% MOISTURE RUN 1 700 60/21.1910/20.07 Briquets appear crushed and brittle. RUN 2 700 60/23.1613/17.35 No great improvement in briquet quality. RUN 3 600 58/23.0511/20.13 Slightly stronger briquets, pressure sensitive. RUN 4 70058/23.35 11/19.89 Quality improved, but pressure sensitive. RUN 5 85058/? 13/? Best looking briquets. RUN 6 600 58/36.71 13/20.92 Goodbriquets, but with cracks. RUN 7 500 58/33 11/? Best briquets but highpressure fluctuations. RUN 8 500 60/22.33 11/19.67 Moderate briquets.RUN 9 400 58/23 11/19.9 About the same as RUN 8. MATERIAL: BENTONITE @7%MOISTURE RUN 1 400 56/24 11/19.6 Good briquets, but not well-filled.Surface had cracks. RUN 2 300 56/24.9 11/21.5 Briquets same as RUN 1,but had fewer surface cracks. RUN 3 300 56/21.8 10/20.7 Briquets wereweaker and not well-filled. More lines generated. RUN 4 300 54/27.011/20.1 Quality improved, briquet was much fuller and strong. RUN 5 30052/20.4 17.1 Best looking briquets. Green strength very high, a bit moreflashing, but break off easily in tumbler. NOTE: Hydraulic pressurefluctuates 300–600 psi indicated depending on material flow from bucketelevator. MATERIAL: BENTONITE @14% MOISTURE RUN 6 300 52/21.86 11/19.03Thicker, stickier material results in better quality briquet:well-filled and high in green strength. There are surface cracks. RUN 7300 58/21.5 11/20.6 Briquets are crumbly and wea, very few arewell-formed. Rough edges on most briquets. RUN 8 300 58/24.4 13/19.3Better briquet than previous runs, some surface cracks, but less thanbefore. RUN 9 300 58/25.1 13/20.3 Run withbelt slippage in mind. Longerrun produced briquets like RUN 8 but a bit more splitting and/or minimalclamshelling. RUN 10 300 58/? 15/? Run to see max feed screw speed.Belts slipped, motor tripped. RUN 11 200 58/? 14/? Same objective andresults as RUN 10, with less pressure to reduce load. RUN 12 200 54/?13/? Same results as RUN 11, this run was made with roll and screw speeddecreased for reduced loading (pressure also reduced). RUN 13 20045/20.9 6/20.0 Objective was to determine minimum speeds and pressures.Fines were generated, not briquets. RUN 14 200 58/29.6 13/20.11 Briquetswere full, but feeder motor trips after short run. RUN 15 400 58/31.313/18.7 Belts slipped immediately, feed motor tripped. RUN 16 30058/24.1 12/21.4 Good briquets, but with some surface cracks and flash.Green strength was high. RUN 17 250 58/30.3 58/21.0 Very good briquetwith some flash, no cracks. Full briquet with high green strength. RUN18 250 60/? 15/? Immediate belt slippage and trip RUN 19 250 58/2311/20.0 Most full briquet of all previous runs, but edges not clean. Nocracks, no splitting, high strength. RUN 20 250 56/22.3 11/21.6 Aboutthe same as RUN 19, but run at a slower capacity. RUN 21 300 58/26.313/19.3 Briquets are satisfactory, but highly sensitive to hydraulicpressure. Higher tendency to show splitting. RUN 22 250 58/22.1 12/21.4Best briquet of all previous trials, but still slightly sensitive tohydraulic pressure, though not problematic. No cracks on surface,consistent quality, high strength. RUN 23 250 60/22.4 13/19 Best briquetfor highest capacity. No cracks or splitting. Consistently good qualityand high strength.

TABLE 3 COALINGA PILOT ABANDONMENT RESULTS Top Well Top Initial Bot. “A”Pt Well Type Case TD Perf Fluid L. Plug Fluid L 60-11A Producer 1 2,6802,360 1,297 2,240 NA 2-8-11A Producer 1 1,660 1,449 — 1,196 NA 3-7-11AProducer 1 1,880 1,166 482 1,465 NA 146-11A Producer 1 1,800 1,604 1,4001,462 NA 45-11A Producer 1 1,600 1,503 1,460 1,407 NA 243-11A Producer 11,800 1,617 1,455 1,487 NA 138-11A Producer 1 1,622 1,432 1,270 1,281 NAAmity 9- Cyclic 1 973 447 355 342 NA 3-1D 8-4A-1D Cyclic 1 605 162 50 1NA 2-8-25D Cyclic 1 1,130 885 720 529 NA 2-7-25D Cyclic 1 1,150 1,006720 810 NA 2-9-7C Cyclic 2 1,820 1,500 1,320 1,372 1,091 1-7-19C Cyclic2 1,900 1,642 — 1,554 1,303 4-8-7C Producer 2 1,800 1,673 700 1,5731,237 4-7-7C Producer 2 1,810 1,681 280 1,558 1,147 4-7-17C Water Inj 33,405 3,278 380 3,141 2,322 3-6-17C Water Inj 3 3,270 3,152 350 2,9852,316 Arica 6- Producer 3 2,095 1,984 — 1,850 1,468 6-7C Arica 5-Producer 3 1,965 1,842 480 1,763 1,382 6-7C Top Fresh T/Fresh Surf. TopAban. Doggr “A” Pt Water Water Fluid Surf. Time Ap- Well Plug Fluid L.Plug L. Plug (hrs) proval 60-11A NA NA NA 480 10 12.5 Yes 2-8-11A NA NANA 504 9 15.5 Yes 3-7-11A NA NA NA — 10 7 Yes 146-11A NA NA NA — 8 11Yes 45-11A NA NA NA 355 11 6.5 Yes 243-11A NA NA NA at 3 6 Yes surf138-11A NA NA NA — 8 4.5 Yes Amity 9- NA NA NA at 11 4.5 Yes 3-1D surf8-4A-1D NA NA NA at NA 4 Yes surf 2-8-25D NA NA NA at 9 7 Yes surf2-7-25D NA NA NA at 1 5 Yes surf 2-9-7C 1,091 at surf 232 at 9 6.5 Yessurf 1-7-19C 1,303 at surf 352 at 11 7 Yes surf 4-8-7C 1,237 at surf 399at 10 7 Yes surf 4-7-7C 1,147 at surf 355 — 10 19.5 Yes 4-7-17C 2,322 98 1,041 — 1 27.5 Yes 3-6-17C 2,316 at surf 1,117 at 13 7.5 Yes surfArica 6- 1,468 106 507 at 8 10 Yes 6-7C surf Arica 5- 1,382 at surf 567— 8 28 Yes 6-7C Note: All depths in feet from ground level

1. A method for forming a material for plugging a well comprising a.obtaining a feedstock comprising bentonite in admixture with aproportion of water to permit the formation of compacted nodules havinga density of at least 2.0 g/cm³ and a mean particle survival at a crushforce of at least 800 newtons and capable of having at least 50%survival when dropped 1.5 meters onto a concrete surface, b. feeding thefeedstock under pressure to a continuous roll press machine underconditions to permit the formation of said compacted nodules and c.recovering the compacted nodules.
 2. The method of claim 1 wherein thefeedstock comprises from about 35% to about 98% by weight bentonite,from about 0% to about 45% by weight nonbentonite solids, and from about2% to about 20% by weight nonconnate water.
 3. The method of claim 1wherein the feedstock comprises from about 45% to about 95% by weightbentonite, from about 0% to about 35% by weight nonbentonite solids, andfrom about 5% to about 20% by weight nonconnate water.
 4. The method ofclaim 1 wherein the feedstock comprises from about 64% to about 88% byweight bentonite, from about 0% to about 20% by weight nonbentonitesolids, and from about 12% to about 16% by weight nonconnate water. 5.The method of claim 1 wherein the feedstock consists essentially of fromabout 85% to about 90% by weight bentonite and from about 10% to about15% by weight nonconnate water.
 6. The method of claim 1 wherein thepressure is a pressure of at least about 1 Mpa.
 7. The method of claim 1wherein the pressure is a pressure of at least about 3 Mpa.
 8. Themethod of claim 1 wherein the pressure is a pressure of at least about 5Mpa.
 9. The method of claim 1 wherein said roller press is operated at aspeed of from about 2 RPM to about 50 RPM.